In clinical chemistry, it is frequently required to carry out the metered application of an analytical liquid to a target. The liquid can be for example a sample fluid, especially blood or serum, a liquid reagent or a calibrating liquid. As a general rule, these liquids contain proteins or other macromolecules participating in biochemical processes.
The target to which the liquid is to be applied can be a reaction vessel, very small plastic reaction vessels being used predominantly in automatic analyzers at the present time. The microtitre plates often used in microbiology are a further example. One case which is of particular importance for the invention is the application of the analytical liquid to an analysis element (frequently also referred to as a test carrier or as a solid state analysis element). In terms of the present invention, this concept includes both discrete analysis elements and bands, strips or other forms of continuous analysis elements which can be passed continuously through a metering station where the analytical liquid is applied.
Traditionally, various forms of plunger-barrel constructions (dispensers and diluters) were used for the application of analytical liquids in automatic analyzers. Reagents were predominantly applied to analysis elements in such a way that a carrier matrix, for example made of paper, was immersed in a liquid reagent or, in a layering method, a reagent film was produced from a film-forming liquid containing polymers. If a spatially delimited reagent domain had to be produced specifically on a base layer, it was recommended to use various printing techniques.
EP-A-119 573 and EP-A-268 237 (U.S. Pat. No. 4,877,745) deal with methods and devices of the type indicated at the outset. Their technique is based on the ink-jet technology originally developed for computer printers (ink-jet printers). Both patent specifications contain more detailed illustrations of the previously known state of the art, to which reference is made here.
EP-A-119 573 deals especially with the problem of providing a cost-effective "pump element" designed as a disposable (single-use) component. The jet chamber here is formed essentially by a section of an elastic tube which is part of the pump element. Directed at its lateral surface is an electromagnetically actuated cylindrical rod which is moved against the tube every time a drop is to be ejected.
EP-A-268 237 describes a device in which the jet chamber consists of a length of tube which is surrounded by a coaxial piezoelectric actuating element, also of tubular design, and which is compressed when a drop is to be ejected.